Electrical signaling



jmp?? @GMM ELECTRICAL SIGNALEJG Filed July 29, 3,235

' two messages are received is always experienced.

g LOUIS COHEN,

, any point Patented Jan. 7,1930

UNITED STATES 0F WASHINGTON, DISTRICT This invention relates to a methodfor theA reception of high frequency signals particularly adapted foruse in signaling over wires which may be either telephone,rtelegraph orpower lines.

The principal object of my invention is to provide methods and meanswhereby several. messages can-be received simultaneously at on a lineover which the signals are transmitted without interfering with eachother.

In the general practice today of the recepf tion of signals, if it isdesired to receive more than one signal atany one station, some form ofelectrical tuning is relied upon to secure selectivity which may besatisactory if the frequencies of the signals to be received are widelyseparated. If, however, the frequencies of the of the signals are notsufficiently wide apart and particularly if more than to be received atthe same point, the tuning methods for obtaining selectivity are notquite adequate. Unlessea very complicated network of circuits isemployed, and in this case the operation of the system would be quitedifficult, a certain degree of interference between the differentmessages In this invention a new principle is introduced securing-ahigher degree of selectivity and rendering the receiving circuits freefrom interference. This is accomplished by the use of simple coupledtuned circuits, and also providing additional circuits in which acurrent iiow is set up of exactly the same character as the current ofthe interfering signal, and coupling this additional circuit to thereceiving circuit in such a way as to neutralize, any residualinterfering effects which canno be eliminated by the process of tuning.If several signals are to be received at the same point, severaladditional circuits are provided, each of which is so adjusted that theeurent flow in each of 'these separate circuits is of exactly the samecharacter in the matter of frequency and phase, and these severaladditional circuits are coupled to the receiving circuit and soconnected as to induce inthe receiving circuit currents in oppositedirections to those produced by the various inter- OF COLUMBIA,ASSIGNOR, BY MESNE AS- TO FEDERAL TELEGRAPH COMPANY, A CORPORATION OFCALIFORNIA SIGNALING 1925. Serial No. 46,831.

fering signals, and thereby completely neutralize the interferingeHec-ts of these various signals which are to be excluded from thereceiving circuit.

Y Let us assume for the purpose of illustration that two signals ofdifferent frequencies f1 and f2 are being transmitted simultaneouslyover the line. At the receiving end of the line two circuits areprovided tuned respectively to the two frequencies. A certain amount'ofcurrent however of thefrequency 2 may find its way into the circuittuned to the frequency f1 and vice versa. 4New, to neutralize theseinterfering currents in the receiving circuit two additional circuitsare provided Awhich are connected to the same point on the lline and soadjusted that the current iiow in these circuits will be of the samecharacter in the matter of phase as the' interfering signal of frequencyf2 will have in the circuit tuned to the frequency f1, and also as theinterfering signal of f1 will have in its operation in the circuit off2. By coupling these auxiliary circuits to-the receiving 'circuits insuch a way as to set up currents in these receiving circuits in oppositedirection to that'produced by the interfering sigmals, the interferenceeffects are completely neutralized.

In the accompanying drawings Figure 1 is a schematic drawing showing anarrangement for thereception of two signals of two dierent frequencies;

Figure 2 is a modification in which an arrangement is shown for thesimultaneous reception of three signals of three dierent frequencies. i

In Figure v1, 1 and 2 represent the end of a line over which the highfrequency signals are transmitted.v A and B are the points on the lineatwhich the receiving system is connected. Reference characters 3 and 4indicate two condensers which permit the high frequency signal currentsto pass but blocking out any low frequency currents which may How on theline. At the junction point between the two condensers 3 and 4, `twotunedreceiving circuits are'connected', one comprising inductance 6 andcondenser 7 connected in series and also connected to ground at thepoint 8, and the other comprising inductance 16, condenser 17, connectedin series, and also connectedto ground at the point 8. Each of these twotuned circuits is separately tuned to be inresonance for one of the twofrequencies of the two signals which are to be received. Each of thesetuned circuits is coupled to a secondary circuit adjusted to be inresonance for the same frequency. vThe circuit 5, 6, 7, 8, is coupled tothe secondary circuit 9, 10, and the circuit 5, 16, 17, 8, is coupled tothe secondary circuit 21, 18, 19. At the terminals of the condensers 10and 19 suitable detectors are connected across the' line represented at20. Now it willbe as- Sumed that the circuit 5, 6, 7, 8, and the circuit9, 10, 11, coupled to it, are tuned toa frequency f1, and that thecircuit 5, 16, 17, 8, and the circuit 18, 19, 21, coupled to it, aretuned to frequency f2 The tuning of these two. circuits may not besuiiicient to separate the Atwo signals completely and a` certain amountof current of frequency f2 may find its way into the circuits tuned tothe frequenc f1 and vice versa. To eliminate these int-er ering effectstwo additional circuits arevprovided connected to the point 5, oneconsistlng of inductance 12, capacity 13, and variable resistance 14connected to ground at a point 8, and the other additional circuit alsoconnected at a point 5 consisting of induc- .tance 22, condenser 23 andvariable resistance 24 and connected to ground at 8. The interferingsignal of frequency f2 producesa cur-` rent flow in the circuit which istuned to f1 of,

a certain amplitude landvphase. To neutralize this effect the additionalcircuit 5, 12, 13, 14, 8, is so adjusted that the current flow of lthefrequency f2 in it will have the same phase as it has in thecircuit-which is tuned to f1. This can be accomplished by the properchoice of the inductance 12, the caacity 13, and the variable resistance14.

he amplitude of the current flow is also determined by these electricalconstants and further the coupling between 12 and 11 can be varied so asto introduce into the circuit 9, 10, an opposite current of exactly thesame magnitude as the interfering current whichis induced in the circuit9, 10, due' to the coupling to the circuit 6, 7, 8. In a similar Waytheadditional circuit 22, 23, 24, 8, is adjusted as to neutralize theinterfering effect of the signal of frequency f1 flowing into the.

circuit 18, 19, 21 which is intended for the reception of the signal ofthe frequency 2.

Figure 2 is a modification of Figure l s owing an arrangement'for thesimultaneous reception of three messages characterized b three differentfrequencies. In this arrangement' there are three separately tunedcircuits each one o-f which is associated with a secondary circuit tunedto the same frequency. For each of these tuned circuits two additionalcircuitsare provided and so adjusted as to neutralize the interferingef- -fects in each one of these circuits which may be produced by theother two signals in exsecondary circuit 11, 9,l 10, 26, another tunedcircuit consisting of inductance 16, capacity- 17 and ground 8,associated with the secondary tuned circuit consisting of 18,' 19, 30,21, and the third tuned circuit consisting of inductance 34, capacit 35and ground 8, associated with the secon ary circuit 39, 37, 36, 45. Foreach of these circuits auxiliary circuits are provided which are coupledto the secondary circuit and these auxiliary circuits are so adjusted inthe matter of amplitude and phase as to neutralize the interferingeffects of the two other signals. I

While I have described my 'invention in certain particular elnbodimentsI desire that it be understood the modifications may be made withoutdeparting from my invention and that I intend no limitations upon theand connectedjto a point on thel line, two

secondary circuits separately coupled to the said tuned circuits, eachof said two secondary circuits including inductance1 and capaclty, anauxiliar Winding in series with said inductance an capacity in each ofsaid secondary circuits, and auxiliary circuits each having aninductance, a capacity and a. resistance unit connected in seriesbetween a. point on the line and the ground, said auxiliary circuitsbeing adjusted in phase by changing the value of said resistance unit,

each of said auxiliary circuits being connected by a variable couplingto one of said secondary circuits so as to induce in said secondarycircuit currents of the same phase and the same amplitude but inopposite direction to those produced by the interfering signals.

2. In a multiplex system for the simultaneous reception of severalhigh'frequency signals transmitted over a line comprising a multiplicityof ,tuned circuitsl connected to a point on the line, each of saidcircuits being tuned to an independent fre uency, a plurality ofsecondary circuits eac comprising an inductance, alcapacity andindependent inductances in series, each of'said independent inductancesbein separately coupled to one of a plurality o auxiliary circuits, eachof said auxiliary circuits comprising an inductance, a capacity and anadjustable resistance unit connected in series and disposed between apoint on the line and-ground, each of said auxiliary circuits beingadjusted in the mat- '5 ter of phase and amplitude to correspond exactly-to the character of the current of selected signals transmittedover said line and so related to the secondary circuit with which theparticular auxiliary circuitv is associated so as to balance outinterfering effects of signals other than those selected by thesecondary circuit. y

8. In a multiplex system for the simultaneous reception of several highfrequency signals transmitted over a line, said system comprising amultiplicity of tuned circuits electrostatically coupled to a point onthe line, each of said circuits being separately tuned to the differenttransmission frequencies andl coupled to a tuned secondary circuit, saidsecondary circuit including an inductance, a capacity, and independentcoupling coils connected in series with said elements and a plurality ofauxiliary circuits each including. adjustable resistance and aAconnection to` ground at one end and to a point on the line at theopposite end, said' auxiliary circuits each corresponding to thefrequencies transmitted over said'line, each of said auxiliary '30circuits being coupledwith one of said independent coupling coils andadjusted to produce therein a current flow of properphase i andamplitude corresponding to a particular interfering signal of one ofsaid frequencies transmitted over said line and so related to thesecondary circuit as to'eliminate therein the effects of that particularinterfering signal,

4. In a multiplex signaling system, a line Wire eircuit a plurality oftuned circuits con- 40 nected to said line wire circuit for receivingIdifferent frequencies transmited over said line Wire circuit, asecondary circuit connected witheach of said tuned circuits, saidsecondary f circuit including an inductance 4l!k and tuning capacity anda plurality of independent inductances corresponding in nurnber to thenumber of signaling frequencies transmitted over said line `wirecircuit, an auxiliary circuit including adjustable :refA sistance,capacity and inductance connected between a point in said line wirecircuit and the ground and individually coupled with a selected one ofthe independent inductances in each of said secondary circuits, saidadjust- 55 able resistance in each of said auxiliary circuits operatingto control the phase relation of the currents in saidvindependentinductances and in the corresponding secondary circuit wherebyinterfering currents in said secondary circuits of a frequency remotefrom the frequency for which the corresponding secondary circuit isadjusted may be neutralized. y In testimony whereof I aix my signature.

LOUIS COHEN.

